Experimental MBI-T Compact Metal Halide

Following on from Osram's pioneering introduction of low wattage metal halide lighting with its double ended lamp, it soon became clear that consumers desired an even more compact light source in this series. The logical progression was to adopt a smaller single ended arc tube design. Thorn Lighting had long since been the leader in single ended metal halide lamps having great experience with its short arc CSI and CID products. Osram was of course the leader in low wattage metal halide products, and the two companies worked together on a new project to create a single ended compact metal halide source based on Osram's low wattage technology and Thorn's single ended experience.

The result was a new range of 150W and 70W single ended products launched by both companies, with Osram also offering a 35W version as well. The lamp shown here is an engineering sample from Thorn Lighting illustrating one of the development stages.

This lamp is one of the first attempts, and is based on the company's 200W CID short arc lamp but with extra sodium dosing to lower the colour temperature. In fact at 2400K it is far too warm and many subsequent developments were necessary to develop the correct chemistry to deliver a stable 3000K output. Electrodes are of solid thoriated tungsten with balled ends. They run parallel to each other in this example but to avoid problems of arcing occurring from the side of the wire rather than the electrode tips, a cranked design was later adopted to increase the spacing below the tips. A steel spring holds the arc tube within the outer bulb, and the lamp is capped with a hot-restrike style GY9.5 two-pin base - later superseded by the G12 cap.